Depending on the requirement of an application, it is sometimes required to connect an electrical device to the same power source via two switching devices or contacting devices. In this case, it is important to provide reliable power to the electrical device. Therefore, an interlock mechanism is provided when the switching devices are used, which means that the switching devices won't be closed simultaneously for avoiding short-circuiting connected electrical devices.
FIG. 6 illustrates a perspective view of a mechanical interlock for interlocking a first and second switching devices according to the prior art, wherein the interlocking mechanism comprising a first and a second housing 60, 60′ connected to each other. The moving contact parts of the switching devices are movable between open and closed positions. A first and a second sliding bar 610, 610′ are arranged on the first housing and second housing respectively and are further connected to the corresponding actuating unit of each of the switching devices. The sliding bars are arranged to slide along a sliding plane defined by an X′- and Y-axis. The Y-axis is defined in the direction of motion of the actuating unit of the switching devices and each of the sliding bars is configured to slide in the Y-axis direction of the sliding plane. The interlock further includes a shaft and a cam integrated with the shaft as one piece 640. This integrated part is disposed between the first and second housing and the cam is configured to be only rotatable when both switching devices are in open position. Furthermore, the cam is adapted, following the motion of the actuating unit and thereby the movable contact part of the first switching device, to rotate to a position wherein for retaining the second switching devices in an open position.
This type of an interlock requires the housings be well connected during operations. During their life, switching devices may however make numerous contacting operations, each of which results a rotation of the cam. The rotations however result in frictions between the shaft-cam assemble and the housings, which consequently results displacement between the housings. This may result in simultaneous closure of both of the switching devices, which consequently results a short-circuit fault. Therefore, a more reliable interlock is desired.